This invention relates to thermoplastic resins made flame retardant by mixing the resin with brominated polyesters, particularly those prepared from tetrabromophthalic anhydride and low molecular weight glycols such as polyethylene glycol, polybutylene glycol and polypropylene glycol; and antimony trioxide.
The theory and practice of using heavily halogenated organic chemical compounds and antimony oxide as additives to produce flame-retarded thermoplastic compositions is a well-known commercial process. The commonly used, highly brominated aromatic organic compounds result in a number of adverse effects to the thermoplastic flame-retarded products.
These adverse effects are (1) poor efficiency; i.e., high levels of bromine and antimony oxide are required to obtain adequate flame retardancy in thin sections; (2) a drastic reduction of overall balance of physical properties, particularly heat distortion and impact strength; and (3) mold buildup of flame retardant during processing and resultant surface degradation of molded parts.